Este trabalho surgiu da percepção dos autores quanto à necessidade de materiais didáticos que pos... more Este trabalho surgiu da percepção dos autores quanto à necessidade de materiais didáticos que possam ser usados como apoio aos estudantes em atividades extraclasse e que, além de criar situações de aprendizagem, sejam também atrativos. Assim, selecionamos para análise um conjunto de videoaulas sobre Ligações Químicas bastante acessadas pelo público. O objetivo foi investigar se essas videoaulas representam um material de apoio adequado a ser usado pelos estudantes do Ensino Médio. A análise dos vídeos mostrou limitações significativas no que se refere aos aspectos técnico-estéticos, à qualidade científica dos conteúdos desenvolvidos e à proposta pedagógica. ensino de química, videoaulas, ligações químicas
This paper presents a revision of the history, definitions, and classification of tracers (natura... more This paper presents a revision of the history, definitions, and classification of tracers (natural and artificial, internal and external). The fundamental ideas concerning tracers are described, followed by their application illustrated by typical examples. The advantages and disadvantages of five classes among the most frequently used external tracers (fluorescent, microbial, chemical, radioactive and activable isotopes) are also described in detail. This review also presents some interesting and modern applications of tracers in the areas of diagnostics in medical practice, environmental pollution, hydrology and petroleum chemistry.
Acta Crystallographica Section E Structure Reports Online, 2008
A natural sample of perovskite (calcium caesium sodium iron titanium oxide) from the Tapira Alkal... more A natural sample of perovskite (calcium caesium sodium iron titanium oxide) from the Tapira Alkaline Complex in southeastern Brazil was found by electron microprobe analysis to have the chemical formula (Ca2+ 0.95 (1)Ce3+ 0.011 (2)Na+ 0.010 (4))(Fe3+ 0.022 (2)Ti4+ 0.98 (1))O2− 3 and by IR spectroscopy to be an anhydrous mineral. Oxygen anions are arranged around Ti4+ in an almost perfect octahedron and around Ca2+ in a distorted 12-fold polyhedron.
The X-ray structure of Na[Lu(DOTA)(H,O)]*4H~O consists of (-1) complex anions balanced by sodium ... more The X-ray structure of Na[Lu(DOTA)(H,O)]*4H~O consists of (-1) complex anions balanced by sodium cations. The ninecoordinate Lu(II1) is linked to the four nitrogen and to four oxygen atoms of the macrocyclic ligand DOTA in a square antiprismatic arrangement with a coordinated water molecule in capping position. In aqueous solution the complex is present under two isomeric forms in the relative ratio of 10: 1, as evaluated from the low temperature limiting t3C NMR spectrum. The variable temperature behavior is consistent with the presence of two dynamic processes. One exchanges enantiomeric pairs for both isomers and involves concerted conformational changes of the ethylenic groups of the macrocyclic ring and rotation of the acetate arms. The other corresponds to the interconversion between the two isomers. Complete line-shape analysis of the variable-temperature t3C NMR spectra of Lu-DOTA allowed a quantitative evaluation of the two processes. The enantiomerization is slower than the isomerization: the corresponding calculated free energies of activation are 65.9 * 1.2, 62.7 f 2.0 (exchange major+minor) and 58.7 f 2.1 kJ molt (exchange minor * major), respectively.
Structural studies and an investigation of the cytotoxic activity of Sn(IV) complexes with N(4)-p... more Structural studies and an investigation of the cytotoxic activity of Sn(IV) complexes with N(4)-phenyl-2-benzoylpyridine thiosemicarbazone (H2Bz4Ph) were carried out. The crystal and molecular structures of [Sn(2Bz4Ph)Cl 3 ]•CH 3 CH 2 OH (1) and [Sn(2Bz4Ph)BuCl 2 ]•H 2 O (Bu = butyl group) (2) were determined. Both compounds present octahedral coordination geometry with the 2Bz4Ph anionic ligand behaving as tridentate on the metal ion. A comparative study of the structures of these compounds along with that of [Sn(2Bz4Ph)Bu 2 Cl] (3) determined before is presented. The cytotoxicity of H2Bz4Ph and its Sn(IV) complexes was investigated against the MCF-7, TK-10 and UACC-62 human tumor cell lines. Among the three complexes, 3 proved to be better as cytotoxic agent than the clinically used drug etoposide. H2Bz4Ph and all complexes were able to induce apoptosis in UACC-62 cells.
Este trabalho surgiu da percepção dos autores quanto à necessidade de materiais didáticos que pos... more Este trabalho surgiu da percepção dos autores quanto à necessidade de materiais didáticos que possam ser usados como apoio aos estudantes em atividades extraclasse e que, além de criar situações de aprendizagem, sejam também atrativos. Assim, selecionamos para análise um conjunto de videoaulas sobre Ligações Químicas bastante acessadas pelo público. O objetivo foi investigar se essas videoaulas representam um material de apoio adequado a ser usado pelos estudantes do Ensino Médio. A análise dos vídeos mostrou limitações significativas no que se refere aos aspectos técnico-estéticos, à qualidade científica dos conteúdos desenvolvidos e à proposta pedagógica. ensino de química, videoaulas, ligações químicas
This paper presents a revision of the history, definitions, and classification of tracers (natura... more This paper presents a revision of the history, definitions, and classification of tracers (natural and artificial, internal and external). The fundamental ideas concerning tracers are described, followed by their application illustrated by typical examples. The advantages and disadvantages of five classes among the most frequently used external tracers (fluorescent, microbial, chemical, radioactive and activable isotopes) are also described in detail. This review also presents some interesting and modern applications of tracers in the areas of diagnostics in medical practice, environmental pollution, hydrology and petroleum chemistry.
Acta Crystallographica Section E Structure Reports Online, 2008
A natural sample of perovskite (calcium caesium sodium iron titanium oxide) from the Tapira Alkal... more A natural sample of perovskite (calcium caesium sodium iron titanium oxide) from the Tapira Alkaline Complex in southeastern Brazil was found by electron microprobe analysis to have the chemical formula (Ca2+ 0.95 (1)Ce3+ 0.011 (2)Na+ 0.010 (4))(Fe3+ 0.022 (2)Ti4+ 0.98 (1))O2− 3 and by IR spectroscopy to be an anhydrous mineral. Oxygen anions are arranged around Ti4+ in an almost perfect octahedron and around Ca2+ in a distorted 12-fold polyhedron.
The X-ray structure of Na[Lu(DOTA)(H,O)]*4H~O consists of (-1) complex anions balanced by sodium ... more The X-ray structure of Na[Lu(DOTA)(H,O)]*4H~O consists of (-1) complex anions balanced by sodium cations. The ninecoordinate Lu(II1) is linked to the four nitrogen and to four oxygen atoms of the macrocyclic ligand DOTA in a square antiprismatic arrangement with a coordinated water molecule in capping position. In aqueous solution the complex is present under two isomeric forms in the relative ratio of 10: 1, as evaluated from the low temperature limiting t3C NMR spectrum. The variable temperature behavior is consistent with the presence of two dynamic processes. One exchanges enantiomeric pairs for both isomers and involves concerted conformational changes of the ethylenic groups of the macrocyclic ring and rotation of the acetate arms. The other corresponds to the interconversion between the two isomers. Complete line-shape analysis of the variable-temperature t3C NMR spectra of Lu-DOTA allowed a quantitative evaluation of the two processes. The enantiomerization is slower than the isomerization: the corresponding calculated free energies of activation are 65.9 * 1.2, 62.7 f 2.0 (exchange major+minor) and 58.7 f 2.1 kJ molt (exchange minor * major), respectively.
Structural studies and an investigation of the cytotoxic activity of Sn(IV) complexes with N(4)-p... more Structural studies and an investigation of the cytotoxic activity of Sn(IV) complexes with N(4)-phenyl-2-benzoylpyridine thiosemicarbazone (H2Bz4Ph) were carried out. The crystal and molecular structures of [Sn(2Bz4Ph)Cl 3 ]•CH 3 CH 2 OH (1) and [Sn(2Bz4Ph)BuCl 2 ]•H 2 O (Bu = butyl group) (2) were determined. Both compounds present octahedral coordination geometry with the 2Bz4Ph anionic ligand behaving as tridentate on the metal ion. A comparative study of the structures of these compounds along with that of [Sn(2Bz4Ph)Bu 2 Cl] (3) determined before is presented. The cytotoxicity of H2Bz4Ph and its Sn(IV) complexes was investigated against the MCF-7, TK-10 and UACC-62 human tumor cell lines. Among the three complexes, 3 proved to be better as cytotoxic agent than the clinically used drug etoposide. H2Bz4Ph and all complexes were able to induce apoptosis in UACC-62 cells.
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Papers by José Ayala